Added androidManifestFileAlias as alias for androidManifestFile to avoid...

... relocating manifest file in IDEA IDE which recognize androidManifestFile configutatuion

This is workaround for this problem with InteliJ IDEA IDE:
http://youtrack.jetbrains.com/issue/IDEA-97807

In short: IDEA use androidManifestFile from plugin configuration and relocate manifest according it. This is OK unless you want to use it only during maven build. Like filter manifest (replace versionName and versionCode) during build and keep original manifest file unmodified.

So I need possibility to change manifest location in the way which IDEA will not understand and will use original location.

So I added androidManifestFileAlias. What do you think about it?